This invention relates to a differential device for use in a vehicle.
In differential devices as disclosed in U.S. Pat. Nos. 4,191,071, 4,491,036 and 4,512,211, a differential function is limited by frictions between the component parts, so that a drive torque applied to that wheel subjected to a larger surface resistance can be made greater than a drive torque applied to that wheel subjected to a smaller surface resistance. Here, the surface resistance means .mu..multidot.W where .mu. represents a coefficient of friction between the road surface and the tire, and W represents a load applied to the tire.
The above conventional differential device comprises a housing to which the torque is transmitted from an engine, and a pair of shafts connected to respective wheels and extending into the housing. The pair of shafts are axially disposed on an axis of rotation of the housing, and one ends of the two shafts are disposed in spaced, opposed relation to each other within the housing. A pair of side gears are connected respectively to the one ends of the two shafts by splines, and therefore a transmission of rotation between each shaft and its mating side gear is achieved. A screw gear portion is formed on the outer periphery of the side gear.
Three openings are formed in the housing and are spaced at equal intervals in the direction of the circumference of the housing. A pair of element gears are rotatably supported in each of these openings. More specifically, a pair of journal pins are removably supported at their opposite ends on the opposed end surfaces of each opening spaced from each other circumferentially of the housing, and the pair of element gears are rotatably mounted on the journal pins, respectively. The axis of rotation of the element gear perpendicularly intersects the axis of rotation of the housing. Each element gear has a screw gear portion and coupling gear portions. The three element gears disposed on one side portion of the housing are arranged around the mating side gear at equal intervals, and the screw gear portions of these element gears are in mesh with the screw gear portion of this side gear. The screw gear portions of the other three element gears disposed on the other side portion of the housing are also in mesh with the screw gear portion of the other side gear. The coupling gear portions of the pair of element gears are in mesh with each other. The differential gear mechanism is constituted by the above intermeshing between the side gears and the element gears and the above intermeshing between the element gears.
In the above conventional differential device (particularly, the device shown in FIG. 4 of U.S. Pat. No. 4,491,036), a washer is interposed between the pair of side gears, and a washer is interposed between each side gear and the housing. In the designing of the differential device, these washers serve to determine the magnitude of the friction between the housing and the side gear as well as the magnitude of the friction between the two side gears, and therefore serve to determine the degree of limiting the differential function of the differential device, thereby performing the function of determining the maximum value of the distribution ratio of the above drive torque.
In the above conventional differential device, when the maximum value of the drive torque distribution ratio is to be changed or adjusted to the optimum value after assembling the differential device, it is necessary to disassemble the differential gear mechanism, to remove the same from the housing, to exchange the washers, and then to again assemble the differential gear mechanism and to mount the same on the housing. Even when only the washer interposed between one side gear and the housing is to be exchanged, it is necessary to remove, from the housing, this side gear, the three element gears in mesh with this side gear, and the shaft spline-connected to this side gear.
Thus, it is very cumbersome to exchange the washers in the once-assembled differential device, and therefore the change or adjustment of the maximum value of the drive torque distribution ratio has been difficult.
U.S. Pat. No. 4,724,721 discloses a differential device provided with support plates. The support plates are supported at their opposite ends on circumferentially spaced, opposed end surfaces of corresponding openings formed in a housing. Each support plate has a pair of support holes. Opposite ends of a pair of element gears are rotatably supported in the support holes of the corresponding pair of support plates. The support plates are inserted into the housing together with the assembled differential gear mechanism along the axis of a tubular portion of the housing. When it is desired to exchange the support plates, the whole of the differential gear mechanism must be removed from the housing.